1. Field of the Invention
Embodiments of the present invention relate to switching electrical power source devices and methods, and in particular to such devices and methods that reduce the hum that is produced in audio equipment.
2. Description of the Related Art
In recent years, there has been a significant progress in the computerization of control systems for switching electrical power source devices. They have become lighter and smaller, and are widely used as the electrical power sources for electronic and electrical devices. An important problem that has been studied involves designing circuits with switching electrical power sources in which the Electro-Magnetic Interference (EMI) noise is reduced.
For example, the Japanese Patent Application Publication (Kokai) Number 2004-236059 describes a noise filter circuit that is used with switching electrical power source devices. FIG. 2 is a block diagram that shows the circuit configuration of a typical switching electrical power source device. The switching electrical power source device 10 comprises an input section 11, a noise filter section 12, a rectification and smoothing section 13, and a converter section 14. An alternating current voltage is input to the input section 11. The external noise that has entered from the input side is eliminated by the noise filter section 12, and then it is rectified and smoothed by the rectification and smoothing section 13. It is then converted into a specified direct current voltage by the converter section 14, and then it is outputted.
A commercial alternating current of, for example, 100 V is supplied to the input section 11 from a commercial alternating current power source and from an alternating current supply line comprising a hot conductor L and a neutral conductor N. A fuse F11 for excess current protection is connected to the hot conductor L.
In the noise filter section 12, a capacitor C11 for the reduction of high frequency noise is connected between the hot conductor L and the neutral conductor N. In the stage following that, a line bypass capacitor C13 for the reduction of high frequency noise is connected between the hot conductor L and a frame ground FG. Together with this, a line bypass capacitor C14 for the reduction of high frequency noise is connected between the neutral conductor N and the frame ground FG.
In the following stage, the choke coil L11 (for the elimination of the common mode noise) is connected between the hot conductor L and the neutral conductor N. In the stage following that, the choke coil L11 and capacitor C12 is connected between the line hot conductor L after the fuse F11 and the neutral conductor N. In addition, in the following stage, a line bypass capacitor C15 is connected between the hot conductor L and the frame ground FG. Together with this, a line bypass capacitor C16 is connected between the neutral conductor N and the frame ground FG.
The line bypass capacitors C13, C14, C15, and C16 in the noise filter section 12 eliminate the common mode noise that is generated by the current that flows through the parasitic capacitor between the collector or the source of the switching element in the DC-DC converter and the frame ground FG.
The alternating current that has passed through the noise filter section 12, after being rectified by a diode bridge D11 in the rectification and smoothing section 13, is smoothed by a capacitor C17 in the rectification and smoothing section 13, and thus becomes an a stable direct current voltage. The a stable direct current voltage is stabilized by the DC-DC converter in the converter section 14, and then becomes a specified direct current voltage for output.
In FIG. 2, in order to simplify the explanation, details of several circuits such as the oscillation start circuit, the oscillator circuit, and the protection circuit have been omitted.